In situ electrolyte replenishment with atmospheric pressure-chemical/electrochemical vapour deposition for molten carbonate fuel cells

Abstract

Molten carbonate fuel cells (MCFCs) offer several advantages in energy applications, but their lifetime is limited especially by electrolyte depletion. In this study, a novel in situ method for replenishing the electrolyte in MCFCs by injecting gaseous electrolyte precursors (EP) that form liquid electrolyte through reactions with CO2/O2 gases or CO32- ions is introduced. The selection of EP species (LiI, NaI, and KOH) are guided by thermodynamic considerations including high vapour pressures and conversion rates to Li/K or Li/Na carbonates. The proposed approach addresses two electrolytic depletion stages: consumption of the electrolyte in the electrode (Stage 1) and in the matrix pores (Stage 2). Atmospheric-pressure electrochemical vapour deposition (AP-EVD) and atmospheric-pressure chemical vapour deposition (AP-CVD) are demonstrated to replenish electrolyte in the electrode and matrix pores, respectively. The applied techniques sustained a cell with a low (Li/Na)2CO3 electrolyte level for long-term operation (>1,000 h) while maintaining stable performance (>0.8 V at 150 mA cm−2). The method also returned an inactive cell to its normal operating conditions (OCV: 1.054 V, RΩ: 0.61 Ω cm2, (Li/K)2CO3 electrolyte). These results promise enhanced durability of MCFCs and render them much more viable for use in energy applications.